T. J. Edwards

Compact source of continuously and widely-tunable terahertz radiation.

We report a THz radiation source based on the technique of non-collinear phasematched parametric generation. The source, which is compact and operable at room temperature, generates nanosecond pulses of peak power and energy greater than 1W and 5 nJ respectively. The radiation is continuously tunable over the range 1.2-3.05 THz and is of narrow spectral bandwidth (<100 GHz). The use of intersecting pump and parametric wave cavities results in threshold pump pulse energies below 1 mJ (from a Nd:YAG laser excited at 20 W, 500 microsec by a quasi-CW diode-laser) and close to 50% down-conversion efficiency when operated at twice threshold.

Line-narrowed, compact, and coherent source of widely tunable terahertz radiation

Parametric down-conversion techniques provide an effective means for producing terahertz radiation. A novel device, based on an intra-cavity geometry, has been developed that is both compact and widely tunable over the range 1-3 THz. Reduction of the free-running linewidth of this device (typically 50-100 GHz) to <5 GHz accompanied by continuous and smooth tuning over a band extending over 50-100 GHz where this band may be set anywhere within the above tuning range is described. A significant increase in the mean terahertz power generated to >10 muW is attained by increasing the pulse repetition rate up to 350 Hz. Applications in spectroscopy and imaging are discussed.

High-power, continuous-wave, singly resonant, intracavity optical parametric oscillator

A high-power continuous-wave optical parametric oscillator based on the nonlinear material KTiOAsO4 and pumped internal to a tunable Ti:sapphire laser is described. The use of the intracavity pumping approach has enabled operation of a singly resonant oscillator (SRO), resulting in the generation of as much as 1.46 W of infrared power in a 11.5-mm-long crystal. Amplitude-stable signal and idler outputs, each in excess of 500 mW, over the respective wavelength ranges of 1.11–1.20 and 2.44–2.86 μm have been extracted from the SRO. We demonstrate up to 90% down-conversion of the optimum Ti:sapphire output power to the SRO, confirming our recent theoretical predictions. The performance characteristics of the device demonstrate that practical, stable, and efficient operation of continuous-wave SROs at watt-level output power can be readily achieved in conventional birefringent materials by exploiting the intracavity pumping approach.

Developing and evaluating animations for teaching quantum mechanics concepts

In this paper, we describe animations and animated visualizations for introductory and intermediate-level quantum mechanics instruction developed at the University of St Andrews. The animations aim to help students build mental representations of quantum mechanics concepts. They focus on known areas of student difficulty and misconceptions by including animated step-by-step explanations of key points. The animations are freely available, with additional resources available to instructors. We have investigated their educational effectiveness both in terms of student attitude and performance. Questionnaires showed that students are on the whole very positive about the animations and make substantial use of them. A diagnostic survey administered to level 2 and 3 students showed that level 2 students significantly outperformed level 3 students on topics which they had investigated using the animations.

High-Bandwidth and Large Coupling Tolerance Graded-Index Multimode Polymer Waveguides for On-Board High-Speed Optical Interconnects

Optical interconnects have attracted significant research interest for use in short-reach board-level optical communication links in supercomputers and data centers. Multimode polymer waveguides in particular constitute an attractive technology for on-board optical interconnects, as they provide high bandwidth, offer relaxed alignment tolerances, and can be cost-effectively integrated onto standard printed circuit boards (PCBs). However, the continuing improvements in bandwidth performance of optical sources make it important to investigate approaches to develop high-bandwidth polymer waveguides. In this paper, we present dispersion studies on a graded-index (GI) waveguide in siloxane materials designed to deliver high bandwidth over a range of launch conditions. Bandwidth-length products of >70 and ~65 GHz×m are observed using a 50/125 μm multimode fibre (MMF) launch for input offsets of ±10 μm without and with the use of a mode mixer (MM), respectively; and enhanced values of >100 GHz×m are found under a 10× microscope objective launch for input offsets of ~18 × 20 μm2. The large range of offsets is within the -1 dB alignment tolerances. A theoretical model is developed using the measured refractive index profile of the waveguide, and general agreement is found with experimental bandwidth measurements. The reported results clearly demonstrate the potential of this technology for use in high-speed board-level optical links, and indicate that data transmission of 100 Gb/s over a multimode polymer waveguide is feasible with appropriate refractive index engineering.

Continuous-wave, singly-resonant, optical parametric oscillator based on periodically poled KTiOPO4.

A continuous-wave singly-resonant optical parametric oscillator (SRO) has been implemented using a 20 mm long crystal of periodically poled KTiOPO4 (PPKTP) intracavity-pumped at room temperature within a Ti:sapphire laser. The device delivers a maximum output power of 455 mW at a non-resonant idler wavelength of 2.47 µm. The 28.5-µm grating PPKTP crystal provides SRO tuning over 1.14–1.27 µm (signal) and 2.23–2.73 µm (idler) limited by optical coating bandwidths and corresponding to a pump tuning range of 805.5–811.2 nm. Temperature tuning of the device generated signal and idler ranges of 1.18–1.26 µm and 2.29–2.57 µm, respectively, corresponding to an average tuning rate of 1.2 nm/degree (signal) and 4.5 nm/degree (idler). Ring-cavity configuration of the device resulted in generation of 115 mW of single-frequency idler output at 2.35 µm.

A new multimedia resource for teaching quantum mechanics concepts

We describe a collection of interactive animations and visualizations for teaching quantum mechanics. The animations can be used at all levels of the undergraduate curriculum. Each animation includes a step-by-step exploration that explains the key points. The animations and instructor resources are freely available. By using a diagnostic survey, we report substantial learning gains for students who have worked with the animations.

Graded-index polymer multimode waveguides for 100 Gb/s board-level data transmission

We report enhanced graded-index multimode polymer waveguides with >70GHz×m for MMF launch and >200GHz×m for restricted launch, indicating the capability of on-board waveguide transmission of >100 Gb/s. Simulations using the measured refractive index profile agree well with the experiments.

Dispersion studies on multimode polymer spiral waveguides for board-level optical interconnects

Dispersion studies are conducted on 1m long multimode polymer spiral waveguides with different refractive index profiles. Bandwidth-length products >40GHz×m are obtained from such waveguides under a 50/125 μm MMF, indicating the potential of this technology.

Compact and coherent source of widely tunable THz radiation

We report a THz radiation source based on the technique of non-collinear phasematched parametric generation. The source, which is compact and operable at room temperature, generates nanosecond pulses of peak power and energy greater than 3 W and 17 nJ respectively. The radiation is continuously tunable over the range 1.2-3.05 THz and is of narrow spectral bandwidth (<100 GHz). The use of intersecting pump and parametric wave cavities results in minimum threshold pump pulse energies below 1 mJ (from a Nd:YAG laser excited at 20 W, 500 μsec by a quasi-CW diode-laser) and close to 50% down-conversion efficiency when operated at twice threshold.